Polyolefin products and process additives therefor having reduced transfer to substrates

ABSTRACT

A process additive for polyolefin films and foams produces products having reduced aging time and reduced greasiness and reduced grease-like transfer as compared to glycerol monostearate (GMS). Carbon dioxide based blowing agents are suitable. The process additive comprises a fatty acid N-aliphatic alcohol amide of the general formula R—CON(R′)R″. R is a fatty hydrocarbon radical having from about 8 to 30 carbons. R′ typically is hydrogen. R′ can also be an alkyl radical of from about 1 to 6 carbons or an alkyl alcohol radical of from about 1 to 6 carbons. R″ is an alkyl alcohol fragment of from about 1 to 6 carbons. The alkyl alcohol fragments can be monohydric or polyhydric. Secondary fatty monoalkanolamides in which R′ is hydrogen are particularly useful, especially stearamide monoethanolamine (MEA). The benefits of the invention can be achieved and enhanced in some examples by mixing the fatty acid N-aliphatic alcohol amide with an ester of a long chain fatty acid with a polyhydric alcohol, including GMS. Examples of fatty acid N-aliphatic alcohol amides include cocamide MEA, lauramide monoisopropylamine (MIPA), oleamide MIPA, and stearamide 2,3-propanediol.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of application Ser. No.09/614,499, filed Jul. 11, 2000 now U.S. Pat. No. 6,232,355 which is adivisional application of application Ser. No. 09/414,397, filed Oct. 7,1999, now U.S. Pat. No. 6,156,813, which is a continuation-in-part ofapplication Ser. No. 08/944,732, filed Oct. 6, 1997, now U.S. Pat. No.6,005,015, all of which are incorporated herein by reference in theirentirety, and claims the benefit of their earlier filing dates.

FIELD OF THE INVENTION

This invention relates to products made from polyolefins and processadditives used in connection therewith. In particular, this inventionrelates to extrudable compositions for producing polyolefin films and toexpandable compositions for producing polyolefin foam products.

BACKGROUND OF THE INVENTION

Various processes and equipment for extrusion foaming of thermoplasticresins have been used for many years. Generally, solid pellets ofthermoplastic resin are fed through a hopper to a melting zone in whichthe resin is melted, or plasticized, to form a flowable thermoplasticmass. The plasticized thermoplastic mass generally is then transportedto a mixing zone where the thermoplastic mass is thoroughly mixed with ablowing agent under pressure for subsequent cooling and substantiallyfree expansion of the resin to form a foam. The blowing agent expandsthe molten mass to form the cells of the foam and the thermoplastic foamis cooled.

The blowing agent gradually diffuses from the cells of the foam and iseventually replaced by air diffusing into the cells. Diffusivity of theblowing agent and the selection and use of appropriate blowing agentsare important aspects of foam manufacture. If the diffusivity of ablowing agent out of the cells of a foam is too fast compared to thediffusivity of air, so that the blowing agent is not replaced by air asit escapes, then the foam typically collapses and is said to havedimensional stability problems. For many years, chlorofluorocarbons(“CFCs”) were used that had excellent diffusivity characteristics andresulted in high quality, dimensionally stable foam products. However,CFCs are no longer acceptable as blowing agents because of globalregulations prohibiting their use.

Other compounds, including lower hydrocarbons, alcohols and ketones,various hydrofluorocarbons, and inert gases have been proposed asalternative blowing agents to CFCs. Some of these compounds diffuse outof the foam cells at a rate that reduces dimensional stability and canresult in collapse of the foam cells. Aging modifiers have beendeveloped for incorporation into polyolefin resins that slow thediffusion of selected blowing agents out of the polyolefin foam cells.These aging modifiers are sometimes referred to as permeabilitymodifiers or stability control agents. Among the various aging modifiersthat have been proposed are the saturated higher fatty acid amides,saturated higher aliphatic amines, esters of saturated higher fattyacids, copolymers of ethylene and unsaturated carboxylic acids, andothers.

One of the more widely used aging modifiers for polyolefin foams isglycerol monostearate. Glycerol monostearate is also added to resins forextrusion to form films. Glycerol monostearate is also called GMS,glyceryl monostearate, and monostearin. GMS is a monoglyceride and is anester of stearic acid, which is C₁₈ acid, and the trihydric alcoholglycerol. GMS is a pure white or cream colored and wax-like solid.

GMS and other similar aging modifiers are thought to coat the walls ofthe foam cells to slow the blowing agent gas from escaping and therebyto prevent collapse of the cells of the foam. However, these agingmodifiers can leave a grease-like residue on the surface of the foamthat can be transferred to objects that come into contact with the foam.The transfer of this grease-like residue to certain substrates isproblematic and is particularly undesirable on optical products and highgloss finishes.

GMS also tends to slow the rate of blowing agent diffusion from thecells to the point that some residual blowing agent is maintained in thecells for an undesirably long period of time after manufacture. Too slowa rate of blowing agent diffusion from the cells of the foam can resultin dimensional stability problems. Foam rolls can become tight instorage.

It would be desirable to provide a foam product in which an acceptableblowing agent would escape from the cells of the fresh foam at a ratethat more closely matches the rate of air entering the cells of the foamto substantially eliminate dimensional changes in the foam upon aging.It would also be desirable to provide foam and other products, includingfilms, in which transfer of grease-like residue to substrates isreduced.

SUMMARY OF THE INVENTION

The invention relates to process additives for polyolefin products thatcan substantially reduce greasy deposits on substrates and, in foams,promotes an increased rate of escape of blowing agent from the cells ascompared to glycerol monostearate (GMS) alone. The process additives areparticularly useful for producing stable foams from carbon dioxide basedblowing agents and reducing the aging time for these foams. The processadditive comprises at least one fatty acid N-aliphatic alcohol amide andcan be a secondary or tertiary amide.

An ester of a long chain fatty acid with a polyhydric alcohol, includingGMS, can be used with the amide, while still achieving the benefits ofthe invention. The two components can be added to the polyolefin resineither in admixture or separately. The amide and the ester have beenobserved to exhibit a substantially single differential scanningcalorimetry (DSC) melting point that varies linearly depending on therelative amounts of amide and ester, thus signifying some chemicalcompatibility. It has also been observed that the transfer ofgrease-like residue is more substantially reduced when both the esterand the amide are present in the polyolefin resin than when the amide isused in the absence of the ester.

Typically the ester and the amide are present in the process additive ina ratio of the ester to the amide of from about 0:1 to 10:1. Thepolyolefin and process additive typically are present in a ratio of fromabout 100:0.01 to 100:5, respectively.

The fatty acid N-aliphatic alcohol amide is a secondary or tertiaryamide having the formula R—CON(R′)R″. R is a fatty hydrocarbon radicalhaving from about 8 to 30 carbons. R′ typically is hydrogen. R′ can alsobe an alkyl radical of from about 1 to 6 carbons or an alkyl alcoholradical of from about 1 to 6 carbons. R″ is an alkyl alcohol fragment offrom about 1 to 6 carbons. The alkyl alcohol fragments can be monohydricor polyhydric. Secondary fatty monoalkanolamides, in which R′ ishydrogen and which have the general formula RCONHR″, are particularlyuseful process additives.

One method of preparing the amide is to react a fatty acid with analkanolamine, especially a monoalcohol amine. The amine group of thealkanolamine is substituted for the hydroxyl moiety of the fatty acidcarboxyl group to form a molecule having a fatty acid amide moiety andan aliphatic alcohol moiety characterized by the attachment of thealcohol moiety to an amide nitrogen. The fatty acid is typically coconutacid, lauric acid, stearic acid, palmitic acid, or oleic acid. Thealkanolamine is typically monoethanolamine (MEA), monoisopropanol amine(MIPA), n-propanolamine, betapropanolamine, or 2,3-propanediol amine. Anexample is the fatty monoalkanolamide stearyl monoethanolamide, whichhas the formula CH₃(CH₂)₁₆CONHCH₂CH₂OH and is sometimes calledstearamide MEA. Another example, in which the alcohol is dihydric, isstearyl 2,3-dihydroxy propyl amide, which is also called stearamide2,3-propanediol and which has the formula CH₃(CH₂)₁₆CONHCH₂CH(OH)CH₂OH.

The invention includes polyolefinic compositions that are films or foamsand compositions for preparing polyolefin foam products in which theabove process additive is incorporated. Typically, the resin is selectedfrom the group consisting of ethylene or propylene homopolymers andcopolymers of ethylene or propylene and a copolymerizable monomer.Stable foams having a relatively short aging time can be prepared fromcarbon dioxide blowing agents, including blends of carbon dioxide withhydrocarbons, including the volatile hydrocarbons.

The invention includes a polyolefin foam product that comprises anexpanded polyolefin made from the foamable composition described above.Grease-like transfer to substrates is substantially reduced as comparedto GMS alone. Aging time is significantly reduced without loss ofstability. Sheet products are useful because sheet products are mosttypically used to protect high gloss finishes, optical products, and thelike. However, the invention is also applicable to plank foam productsand to films.

Thus the invention provides a process additive that can function as aneffective aging modifier, a foamable composition containing the processadditive, and a polyolefinic foam made from the foamable composition.The foam exhibits reduced grease-like transfer to substrates and isdimensionally stable. Aging time is significantly improved and can bereduced by as much as half or more. Carbon dioxide blowing agents can beused. The invention also provides extrudable composititons and filmsmade from them that incorporate a process additive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Some of the features and advantages of the invention have been stated.Other advantages will become apparent as the description of theinvention proceeds, taken in conjunction with the accompanying drawings,in which:

FIG. 1 is a plot of absorbence at various wavelengths for severalprocess additives at 2 percent concentration by weight in a 2 mil thickpolyethylene film, including a process additive according to theinvention;

FIG. 2 is a plot showing a concentration of glycerol monostearate (GMS)on the surface of a foam and as transferred to a highly polished KBrwindow with which the foam has come into contact;

FIG. 3 is a plot showing the effect of an increase in concentration ofGMS in polyethylene foams on its absorbence at various wavelengths;

FIG. 4 is a plot comparing the property of grease-like transfer forvarious process additives. A commercially available GMS is given thevalue of 1;

FIG. 5 shows that the grease-like transfer increases with increasingconcentration of GMS;

FIG. 6 is a plot comparing absorbance peaks for several process additivecompositions;

FIG. 7 is a plot comparing absorbance peaks for several process additivecompositions; and

FIGS. 8 and 9 are plots of the percentage of the lowest explosive limit(% LEL) over time for polyethylene foams prepared with the processadditives of the invention.

DETAILED DESCRIPTION

Various compounds were evaluated quantitatively as process additives forgrease-like transfer to substrates by high performance Fourier-transforminfrared spectroscopy (FT-IR). Plots are shown in FIGS. 1 through 3, 6,and 7 of the fraction of absorbence in the mid-infrared region forparticular compounds of interest. Infrared radiation is recorded in thecustomary units of wavenumbers, which are oscillations per centimeterand are read as reciprocal centimeters. The mid-infrared region of fromabout 200 to 4,000 cm⁻¹ corresponds to wavelengths of light of fromabout 50 to 2.5 microns.

Spectroquality potassium bromide (KBr) crystal was chosen as a usefulcandidate for studying grease-like transfer from a foam surface to aglass-like or highly polished substrate. KBr crystal typically is usedin FT-IR spectroscopy. KBr crystal absorbs no infrared light in thespectrum from 4000 to 400 cm⁻¹, which are the wavenumbers of interest.KBr crystal was used in all of the examples shown below except asotherwise noted, and is sometimes referred to below as “glass.”

Chemical formulas for various compounds that were analyzed by FT-IRspectroscopy, including a compound in accordance with the invention, areshown below in Table 1 and are identified in the Figures by letter codesA through H. Kemamide S-180(C), Kemamide S(D), Alkamide S-280(E),Alkamide L-203(F), and Alkamide LIPA are tradenames for variouscommercial products corresponding to the formulas and letter codes asshown in Table 1. SAPD designates stearamide 2,3-propanediol. TheKemamides are available from Humko Chemical Division of WitcoCorporation, which is located in Memphis, Tenn. The Alkamides areavailable from Rhone-Poulenc, which is located in Cranbury, N.J. SAPDwas made by and is available from Rhone-Poulenc by special request.Alkamide S-280, Alkamide L-203, Alkamide LIPA, and SAPD are all examplesof compounds useful as process additives in accordance with theinvention.

There are two principal grades of glycerol monostearate (GMS) used inthe plastics industries as process additives, including aging modifiers.One grade, identified below as “B” in Table 1, is derived fromhydrogenated tallow that contains about 65 percent stearic acid radicalsand about 30 percent palmitic acid radicals. The tallow is esterifiedwith glycerol and typically contains about 56 percent monoester, 37percent diester, and 7 percent of the triester. This grade of GMS iswhat is typically referred to commercially as “GMS” or as glycerolmono/distearate. It is available from Witco Corporation, Humko ChemicalDivision, Memphis, Tenn., under the designation Atmos 150. It is alsoavailable under the designation Pationic 1052, which is sold by theAmerican Ingredients Company, Patco Polymer Additives Division, KansasCity, Mo.

Another grade of GMS is the distilled ester, d-GMS, which is identifiedas “A” in Table 1, Distilled GMS typically contains about 96 percent ofthe monoester. Distilled GMS is available under the designations Atmer129 and Pationic 902 from Witco and Patco, respectively, whose locationsare given above.

TABLE 1 COMPOUND FORMULAS Letter Code Name Formula R Group A DistilledGlycerol R—COOCC(OH)COH Stearyl Monostearate, 96% B Glycerol Mono/R—COOCC(OH)COH, 55% Stearyl distearate (R—COOC)₂COH, 37% C KemamideS-180 R—CONHR Stearyl D Kemamide S R—CONH₂ Stearyl E Alkamide S-280R—CONH—C—C—OH Stearyl F Alkamide L-203 R—CONH—C—C—OH Lauryl G AlkamideLIPA R—CONH—C—C(CH₃)OH Lauryl H SAPD R—CONH—C—C(OH)COH Stearyl

As can be seen from Table 1, compounds E and F, which are useful asprocess additives in accordance with the invention, are stearyl- andlauryl-monoethanolamide, respectively. These compounds are also calledstearamide monoethanolamine (MEA) and lauramide MEA, respectively.Stearamide MEA can be represented by the formula CH₃(CH₂)₁₆CONHCH₂CH₂OH.Lauramide MEA can be represented by the formula CH₃(CH₂)₁₀CONHCH₂CH₂OH.

Compounds G and H are also useful as process additives of the invention.Compound G is a lauryl monoisopropanol amide and is sometimes referredto as lauramide monoisopropanolamine (MIPA). Compound H is an exampleprepared from a dihydric alcohol amine, 2,3-propanediol amine.

These fatty monoalkanolamide compounds have the general formulaR—CON(R′)R″, in which R is the stearyl or lauryl group, respectively, R′is H, and R″ is an alcohol moiety, ethanol, isopropanol, or2,3-propanediol moiety.

It is observed that complex molecules of the general formula have ahydrophobic end in the R group that is separated from a hydrophilic endin the R″ group. While not wishing to be bound by theory, it is believedthat the distinct functionalities of the hydrophobic and hydrophilicportions of the compound may be at least partially responsible for thefavorable characteristics of these compounds as process additives, and,in particular, as aging modifiers.

Generally, the process additives of the invention that have thesedistinct hydrophilic and hydrophobic functionalities comprise at leastone fatty acid N-aliphatic alcohol amide. The substituted amide can beeither a secondary amide or a tertiary amide and typically will have theformula R-CON(R′)R″.

These compounds are complex molecules having an amide functional moietyand at least one alcohol functional moiety. These compounds arecharacterized by the aliphatic alcohol moiety R″ attached to an amidegroup nitrogen and a hydrocarbon group R attached to the carbon of theamide group.

R generally can be any fatty hydrocarbon group of from about 8 to 30carbons to provide a distinct hydrophobic component of the compound. Thepreferred fatty portion of the amide is lauryl, stearyl, palmityl, oroleyl, because these are the most economical to use. It should beunderstood that many commercial grades of fatty acids that may be usedto prepare the process additives of the invention are mixtures andtypically are not of one pure acid, even though these acids are commonlycalled by the predominant acid present. For example, commercial gradestearic acid typically has palmitic acid in it. Coconut acid, from whichcocamide MEA and similar compounds are derived, typically has a varietyof acid chain lengths present that vary from 6 to 18 carbons, but ismostly 10, 12, and 14 carbons.

R′ is selected from the group consisting of hydrogen, an alkyl radicalof from about 1 to 6 carbons, and an alkyl alcohol or glycol radical offrom about 1 to 6 carbons, with the hydroxyl moiety on any carbon in thegroup. Compounds in which R′ is hydrogen are useful and normally areless expensive.

The aliphatic alcohol portion, R″, of the amide in Alkamide S-280 andL-203 is an ethanol moiety. However, other alcohols, both monohydric andpolyhydric, and having related properties and sufficient chain length inthe structure should be useful, although not necessarily with equivalentresults. The alcohol provides a distinct hydrophilic portion of thecompound and should not introduce a significant hydrophobic portion. Forexample, Alkamide LIPA and SAPD have an R″ portion of isopropyl alcoholand 2,3-propanediol, respectively.

R′ and R″ can be any monohydric or polyhydric alkyl alcohol radical offrom about 1 to 6 carbons. R′ usually is hydrogen and R″ typically willbe a monohydric or polyhydric alkyl alcohol moiety that has from about 1to 6 carbons. Typically a monohydric alkyl alcohol moiety will beselected from the group consisting of methanol, ethanol, propanol,isopropanol, butanol, pentanol, and hexanol moieties, and in anyisomeric form. A polyhydric alcohol moiety typically will be selectedfrom the group consisting of glycols and glycerol. Ethanol, isopropyl,or dihyroxy propanol moieties are useful.

Typically, for economic reasons, the fatty acid N-aliphatic alcoholamide will be the reaction product of a fatty acid and an alkanolamine.The fatty acid can be any of those having from about 8 to 30 carbons,and will usually be either coconut acid, lauric acid, stearic acid,palmitic acid, or oleic acid. The alkanolamine can be a primary amine,including ethanolamine, isopropanolamine, propanolamine, 2,3-propanediolamine, betapropanolamine, and others.

FIG. 1 is a plot of mid-infrared absorbance at various wavenumbers forseveral compounds B, C, D, and E as identified in Table 1. Theabsorption level changes with the thickness of the film sample and theinfrared absorption characteristics of the particular compound. However,the values shown on the plot of FIG. 1 have been normalized according tofilm thickness. The area under each peak corresponds to the amount ofthe compound that is present in the sample. FIG. 1 and similar plots canbe used as the basis for determining the relative grease-like transfercharacteristics of various compounds when used in foam production forapplication to glass-like and highly polished surfaces, as explainedfurther hereinbelow.

All of the compounds shown in FIG. 1 are at a two percent concentrationin a low density polyethylene resin that has been extruded to a film.The peak at 1730 cm⁻¹ for compound B is for a film that containscommercial GMS process additive, which is typically used as an agingmodifier and is also used as a slip agent for providing lubricity in theextruder. Three separate peaks are identified at 1650 cm⁻¹ for compoundsC, D, and E. The peak labeled E is for Alkamide S-280, which is stearylmonoethanolamide and is an example of an aging modifier in accordancewith the invention in a low density polyethylene resin that has beenextruded to a film. Additional peaks are labeled C for Kemamide S-180and D for Kemamide S, each of which is in a low density polyethyleneresin that has been extruded to a film.

FIG. 2 shows the foam surface peak and the glass transfer peak for aconcentration of 1.2 percent of commercial grade GMS in a low densitypolyethylene resin that was extruded to form a foam of density 1.3pounds per cubic foot. The foam surface and glass transfer peaks, whichare at 1730 cm⁻¹, correspond to a carbonyl group in the GMS structure.The large foam surface peak shows absorption in the infrared spectrumdue to the presence of GMS aging modifier on the foam surface. Thesmaller transfer peak shows absorption in the infrared spectrum that isdue to GMS aging modifier that has been transferred from the foamsurface to the KBr window, which provides a glass-like or highlypolished surface.

Quantitative measure of GMS on the surface of the foam and on thesurface of the window is obtained by integrating the area under thecorresponding peak. The ratio in the area calculated under the two peaksshows the amount of transfer from the foam surface to the window and isa measure of the grease-like transfer of the process additive from thefoam.

Table 2, below, shows data obtained in accordance with the procedureoutlined for FIGS. 1 and 2 that indicates the grease-like transfercharacteristics of a variety of process additives. The data plotted inFIG. 2 corresponds to Example 7 in Table 2, which is a commercial gradeGMS and is the benchmark for grease-like characteristics and grease-liketransfer.

For each example in Table 2, a circular KBr window of one-inch diameterwas placed on the surface of a sample of a thin, light weightpolyethylene foam. The sample was maintained in an oven at 32°Centigrade for one day. A slight load of about 0.06 to 0.12 lb_(f)/in²was applied to the window to simulate packaging conditions in which aproduct having a glass-like or highly polished surface is packaged in athin, light weight polyethylene foam. Thereafter, the KBr crystal wasremoved from the oven and analyzed to show the amount of compoundtransferred to the surface of the crystal.

Each sample was subjected to FT-IR analysis and curves of absorbanceversus wavenumber were generated. The area under the peak at 1730 cm⁻¹was integrated to calculate the amount of compound that was transferredto the surface of the crystal. The ratio of the amount of compoundtransferred to the crystal surface to the amount of compound originallyon the surface of the foam was determined. This ratio was thenmultiplied by 100 to convert it into a percentage of transfer ofcompound from foam to glass. The above procedure was repeated for all ofthe compounds shown in Table 2.

TABLE 2 Melting % Transfer % point of of additive % Example Foam TypeConcentration additive from foam Greasiness % Reduction No. Additive(thickness) of Additive ° C. to glass Level in Greasiness Comments 1 BBlack (⅛″) 0.4 60 16.1  66 34 Greasy# 2 B Black (⅛″) 0.4 60 5.7  24 76Greasy 3 A White (.094″) 1.2 60 17.0  70 22 Greasy 4 A White (.094″) 0.660 11.6  48 57 Greasy 5 A White (.094″) .043 60 9.4  39 61 Greasy 6 AWhite (0.08″) 0.3 60 8.9  37 56 Greasy 7 B White (.074″) 1.2 60 24.2 100 0 Greasy 8 E White (.085″) 2.0 92 3.3  6 94 Good* 9 F White (.075″) 2.082 3.6  7 93 Good 10  F White (.091″) 2.0 82 2.6  5 95 Good 11  H White(0.9″) 1.0 98 4.2  10 90 Good #Greasy-like transfer clearly visible tothe naked eye *No transfer visible to the naked eye at test conditions

The results calculated for the percent transfer of various additivesfrom foam to glass is shown in Column 6 of Table 2. The percent transferof additive from foam to glass for the benchmark Example 7 is calculatedbased on the peak area from FIG. 2 to be 24.2 percent. The grease-liketransfer factor is calculated as the percent transfer of a particularadditive divided by the percent transfer of the benchmark additive. Thebenchmark additive is the commercial grade GMS, so the greasiness factorfor this particular GMS is 1.0. The percent reduction in grease-liketransfer is reported in Column 8 of Table 2.

Example 1 was with the same GMS additive used in Example 7, but at a 0.4percent concentration rather than at a 1.2 percent concentration. Thegrease-like transfer factor, expressed as a percentage of greasiness,was only 66 percent for a 16.1 percent transfer of additive from foam toglass, which shows that the amount of grease-like transfer of anadditive is also dependent upon the concentration of the additive in theresin from which the foam is made. FIG. 3 shows the effect ofconcentration of process additive in a plot of absorbance versuswavenumber for GMS at various concentrations.

Table 2 shows clearly that the use of compounds E and F as processadditives, which are stearamide and lauramide MEA, respectively,produces a superior grease-like transfer factor with low percenttransfer of the additive to the glass and a high reduction ingrease-like characteristics.

The greasiness factor calculated for various compounds at differentconcentrations is shown graphically in FIG. 4 with the GMS additive ofFIG. 2 and Example 7 as the benchmark having a grease-like transferfactor of 1. The Alkamide S-280 additive of Example 8 is shown to have agrease-like transfer factor of only 6 percent by comparison to the GMSaging modifier of Example 2. Alkamide L-203 as shown in Examples 10 and11 also has low grease-like transfer factor.

Kemamide S-280 (C, Table 1) is shown in FIG. 4 to have a grease-liketransfer factor of 31 percent and Kemamide S (D, Table 1) has beendetermined to have a similar grease-like transfer factor when comparedto GMS. Kemamide S-280 and Kemamide S are secondary and primaryaliphatic amides, respectively, and do not include an alcohol moiety asdo the process additives of the invention. Kemamide S-280 and S inadmixture with GMS show two distinct melting points, one for the amideand one for the ester, which does not indicate chemical interactionbetween these amides and GMS. While not wishing to be bound by theory,it is believed that Kemamide S-1 80 and Kemamide S merely dilute thegreasines transfer factor for GMS, in distinction to compounds E and Fof the invention, as shown in Table 2 and in FIG. 4 (Alkamide S-280 andAlkamide L-203, respectively).

FIG. 5 is a plot of grease-like transfer factor versus concentration forGMS and shows that the grease-like transfer factor increases withincreasing concentration based on Examples 4, 5, and 6 of Table 2.

Table 3 shows 13 examples of various low density polyethylene resinsused to prepare lightweight foams with various process additives.Examples 12 through 15 use a concentration of 1.3 percent by weight of acommercial GMS as the benchmark examples. Examples 16 through 22 areprepared with a mixture comprising 60 percent GMS and 40 mole percentAlkamide S-280. This mixture exhibits a single melting point of 72°Centigrade, which is some 12° Centigrade above the melting point for acommercial GMS, which is compound B, Table 1. The single melting pointis thought to signify some chemical interaction between the components.Example 23 is prepared with 1 percent percent GMS and 1.3 percent SAPDby weight. The total amount of the process additive is accordingly by2.3 percent by weight of the resin and comprises 44 percent GMS and 56percent SAPD. Example 24 is prepared with 0.5 percent percent GMS and0.5 percent SAPD by weight for a 50/50 blend of GMS and SAPD at 1percent of the resin by weight.

As can be seen, the standard FT-IR test shows that the grease-liketransfer level of the foams was substantially reduced or eliminated ascompared to GMS used alone. The foam samples of Table 3 were evaluatedby heating in an oven at 40° centigrade for 24 hours in contact with KBrglass windows. Negligible levels of grease-like transfer were achievedwhen GMS was mixed with stearyl monoethanolamide (stearamide MEA).

TABLE 3 Thickness, Foam Aging Modifier % % Greasiness Peak Exampleinches Density, pcf wt. percent Transfer Level# Area 12 0.95 1.22 1.3% A21.8 90.0% 1.210 13 0.112 1.10 1.3% A 21.6 89.2% 1.200 14 0.085 1.291.3% A 23.6 97.5% 1.313 15 0.101 1.27 1.3% A 36.6 151.2% 2.035 16 0.1191.17 1.7% A/E mix† 0.9 3.7% 0.050 17 0.125 1.07 1.7% A/E mix 1.3 5.8%0.075 18 0.099 1.06 1.7% A/E mix 1.3 5.8% 0.075 19 0.059 1.3 1.7% A/Emix 0.7 2.9% 0.038 20 0.065 1.26 1.7% A/E mix 0.9 3.7% 0.050 21 0.0601.21 1.1% A/E mix <0.7 <2.5* <.03 22 0.060 1.40 1.5% A/E mix 4.9 19.6.25 23 0.092 1.36 2.3% A/H mix** 7.3 30.3 .40 24 0.095 1.37 1.0% A/Hmix## 7.2 30.0 .40 †A/E mix is a 60:40 mixture by weight percentcomprising Additives A and E (Table 1). #Benchmarked with 1.3% AdditiveA in absolute values. *Limit of method of detection is 2.5% greasinesslevel with GMS control arbitrarily set at 100%. **A/H mix is a 44:56mixture by weight percent comprising additives A and H (Table 1). ##A/Hmix is a 50:50 mixture by weight percent comprising additives A and H(Table 1).

FIG. 6 shows a plot for Examples 12 through 20 of Table 3 of absorbanceversus wavenumber, which gives an indication of the grease-like transferproperties of the foam product. Examples 16, 17, 18, 19, and 20, whichare examples of the invention, show negligible grease-like transferproperties and virtually no peak.

Table 4, below, shows nine examples of the use of various compounds asprocess additives in thin foam sheets. Example 26 is the control examplein which 1.3 percent of GMS was used as the process additive. Examples27, 28, and 29, which are examples of the invention, show a mixturecomprising 1.3 percent GMS with from 0.6 to 0.8 percent stearamide MEA.Examples 27 through 29 show a clean foam with substantially nogrease-like transfer visible to the unaided eye. The results for each ofthese five examples is plotted in FIG. 7.

Examples 30 through 33 are also examples of the invention. Example 30 issimilar to Examples 27 through 29 and shows a clean foam withsubstantially no detectable grease-like transfer. Examples 31, 32, and33 show a mixture of GMS and Alkamide LIPA (Example 31) and SAPD(Examples 32 and 33) in the volume percentages shown in Table 4 for eachingredient. These additives resulted in foams that are only sightlygreasy and have a low transfer percentage compared to GMS alone.

TABLE 4 Ex- Foam am- Density, % Greasiness % Visual ple Aging Modifierpcf (from FT-IR) Transfer Comments 25 1.3% A 1.17 20.7 86.6 Greasy 261.3% A 1.35 23.9 100 Greasy 27 A/E mix† 1.19 1.7 4.9 Clean, greaseless28 A/E mix 1.74 1.1 4.6 Clean, greaseless 29 A/E mix 1.55 1.1 4.6 Clean,greaseless 30 1.1% A/E mix 1.2 <0.7 <2.5 Clean 31 1.5% A/G mix* 1.4 4.919.6 Slightly Greasy 32 2.3% A/H mix# 1.36 7.3 30.3 Slightly Greasy 331% A/H mix** 1.37 7.2 30.0 Slightly Greasy †A/E mix is a 60:40 mixtureby weight % comprising Additives A and E (Table 1). *A/G mix is a 67:33mixture by weight % comprising Additives A and G (Table 1). #A/H mix isa 44:56 mixture by weight % comprising Additives A and H (Table 1).**A/H mix is a 50:50 mixture by weight % comprising Additives A and H(Table 1).

The fatty acid N-aliphatic alcohol amide provides suprisingly excellentresults in the reduction of grease-like transfer in low density foams ascompared to traditional aging modifiers such as a GMS. However, asobserved above, when used in admixture, GMS and the fatty acidN-aliphatic alcohol amide can produce an even greater reduction ingrease-like transfer from foams. The addition of a small amount of thefatty acid N-aliphatic alcohol amide to a GMS process additive canproduce significant reduction in the grease-like transfercharacteristics of a foam.

The two compounds exhibit a single melting point when used in admixture,which signifies some chemical interaction and may be responsible for theimproved results. The single melting point that is exhibited by themixture of the amide and the ester varies depending on the ratio of theester to the amide and the aging modifier. The melting point decreaseslinearly as the ratio of the ester to the amide increases.

GMS has the structure of an ester of a long chain fatty acid with apolyhydric alcohol. Other esters of long chain fatty acids withpolyhydric alcohols have similar properties and should be useful in thepractice of the invention. Typically, the ester will be a glyceride, andsomewhat more typically, a monoglyceride. The polyhydric alcohol thatcomprises the ester typically will be a trihydric alcohol. Where theester is glycerol stearates, the glycerol monostearate can be eitheralpha glycerol monostearate, beta glycerol monostearate, or mixturesthereof with glycerol di- or tri- stearates. Typically, the ester shouldbe present in the aging modifier in a ratio of the ester to the fattyacid N-aliphatic alcohol amide of from about 0:1 to 10:1.

The GMS and fatty acid N-aliphatic alcohol amide components are presentin the aging modifier in a ratio of the GMS to the amide of from about0:1 to 10:1. A ratio of the ester to the amide of about 2:1 is useful.

The foams are prepared by incorporating the aging modifier components ina polymeric composition and then expanding the polymeric composition.The polymeric composition will normally comprise a polyolefinic resin.The polyolefinic resin can be formed from ethylene or propylenehomopolymers or copolymers of ethylene or propylene and acopolymerizable monomer. The aging modifier will typically be present inthe polymeric composition in a ratio of the polyolefin resin of theaging modifier of from about 100:0.01 to 100:5. A ratio of a polyolefinto aging modifier of about 100:0.5 to 100:3 may be somewhat moretypical.

The polymeric composition will also comprise a blowing agent. Any of theblowing agents known in the art should be useful in the practice of theinvention. However, it normally is not desirable to use those blowingagents that are being phased out because of governmental regulation. Theblowing agent typically will be an inert gas or a hydrocarbon havingfrom 1 to 6 carbons, or mixtures thereof. Any of the inert gases andhydrocarbon blowing agents should be useful in the practice of theinvention, including carbon dioxide, either alone or in an admixturewith a hydrocarbon blowing agent. The process additive of the inventionis particularly useful in part because the additive promotes anincreased rate of blowing agent escape from the cells of the foam ascompared to GMS alone. Thus, aging time is reduced and foam stability ispromoted.

FIGS. 8 and 9 show reduced aging times for foams of the invention. FIGS.8 and 9 are plots of the percentage of the lowest explosive limit (%LEL) over time for two different blowing agents for polyethylene foamprepared with a process additive of the invention. The % LEL is ameasure of the least amount of a hydrocarbon dispersed in air that isexplosive if exposed to a spark or flame. It is desirable to reduce the% LEL to acceptably low values below 100% prior to storing the foam in aconfined space.

The blowing agents were 100% propane and a blend of about 75% propaneand 25% carbon dioxide. Rolls of expanded sheet foam prepared with theseblowing agents in accordance with the invention were aged in awarehouse, as described below. The aged foams were placed in a trailerof the type in which the foams are commonly transported by a tractor andtrailer combination. The trailer was 35 feet long and was filled to 85%of capacity to simulate actual loading conditions. The test was staticin that the trailer did not move. Once in travel, the free flow of airthrough a trailer tends to reduce the % LEL as compared to staticconditions.

The % LEL was determined over time inside the trailer at 6 inches abovethe bottom of the trailer, since propane is heavier than air. The % LELis plotted in FIGS. 8 and 9 against time, temperature, and humidity foreach of the blowing agents. As is shown in the plots of FIGS. 8 and 9,in all cases the % LEL remains below 16 %. FIG. 8 is at the trailernose; FIG. 9 is at the center.

The foam sheets were prepared on a production system having a primaryextruder of diameter 8.9 cm and a secondary extruder of diameter 11.4cm. A resin of low density polyethylene (“LDPE”) was foamed at a rate of205 kg/hr.

An alcoholamide processing additive of the invention, stearamidemonoethanolamine, was added at 0.63 kg/hr and GMS was added at 1.47kg/hr.

The fresh rolls of foam sheet prepared with 100% propane blowing agentwere aged in a warehouse for 6 days. Normally, aging could be expectedto take from about 10 to 12 days to reduce the lowest explosive limit toacceptable levels for foams prepared from GMS alone and a 100% propaneblowing agent. The % LEL is desirably reduced at least to about 50%. Ascan be seen in FIGS. 8 and 9, the % LEL for the propane foam was fromless than 12 to about 16 at the beginning of the trailer test and afteronly 6 days of warehouse aging, and remained even lower thereafter.

Unlike volatile hydrocarbons, carbon dioxide based blowing agentstypically escape so quickly from foam that problems of collapse aresomewhat common. However, the processing additive of the invention iscapable of producing stable, high quality polyolefin foams of reducedaging time from carbon dioxide blowing agents.

It is generally useful to mix the carbon dioxide with a hydrocarbonhaving from 1 to 6 carbons, or mixtures thereof. For the plots of FIGS.8 and 9, LDPE foam sheet of the invention was prepared with a blowingagent mixture of 27% of carbon dioxide and 73% propane, by weight. Itshould be recognized that “mixture” does not necessarily mean the carbondioxide and propane were physically mixed prior to adding to thepolyolefin resin, although premixing can be accomplished if desired.

In the examples of FIGS. 8 and 9, carbon dioxide was added at the rateof 5.1 kg/hr and propane was added separately at a rate of 15.6 kg/hr.The solution of polymer melt and gas was cooled to less than 110° C. andexpanded through an annular die orifice to form a sheet. The foam had adensity of 17.6 kg/cubic meter and was 3.2 mm thick. The sheet was woundon a roll for storage and was aged in a warehouse for 2 days prior tothe trailer test. On the third day, the foam was placed in the trailer.The % LEL during the trailer test never rose above about 5 to 10%.

The combination of carbon dioxide and volatile hydrocarbon blowing agentis particularly advantageous when practiced in connection with thepreparation of foams from resins having the processing additive of theinvention. These foams have excellent stability and significantlyreduced aging time as compared to foams prepared using GMS alone as aprocessing additive.

The above invention has been described with respect to particularpreferred embodiments. However, the foregoing description is notintended to limit the invention to the illustrated embodiments and theskilled artisan should recognize that variations can be made within thespirit and scope of the invention as described in the foregoingspecification. The invention includes all alternatives, modifications,and equivalents that may be included within the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A process additive for polyolefins comprising atleast one fatty acid N-aliphatic alcohol amide, wherein the amide issecondary or tertiary, and an ester of a long chain fatty acid with apolyhydric alcohol, wherein said ester and said amide are present insaid process additive in a ratio of said ester to said amide of fromabout 0:1 to 10:1.
 2. The process additive of claim 1 having asubstantially single melting point that varies depending upon the ratioof said ester to said amide in said aging modifier.
 3. The processadditive of claim 1 wherein said amide is a secondary amide.
 4. Theprocess additive of claim 1 wherein said amide is a fatty monoalkanolamide.
 5. The process additive of claim 1 wherein the fatty acid portionof said amide has from about 8 to 30 carbons.
 6. The process additive ofclaim 1 wherein the fatty acid portion of said amide is selected fromthe group consisting of coconut, lauric, palmitic, stearic, and oleicmoieties.
 7. The process additive of claim 1 wherein the aliphaticalcohol portion of said amide is a monohydric alkyl alcohol moiety offrom about 1 to 6 carbons.
 8. The process additive of claim 7 whereinsaid monohydric alkyl alcohol moiety is selected from the groupconsisting of methanol, ethanol, propanol, butanol, pentanol, andhexanol moieties, and isomers thereof.
 9. The process additive of claim1 wherein the aliphatic alcohol portion of said amide is a polyhydricalcohol moiety of from about 1 to 6 carbons with from 2 to 5 hydroxylmoieties.
 10. The process additive of claim 9 wherein said polyhydricalcohol moiety is a glycol radical.
 11. The process additive of claim 1wherein said amide is selected from the group consisting of fattymonoethanolamide, fatty 2,3 dihydroxy propyl amide, and fattyisopropanol amide.
 12. A process additive for polyolefins comprising anester of a long chain fatty acid with a polyhydric alcohol and amolecule having the structure R—CON(R′)R″ wherein R is a fattyhydrocarbon radical having from about 8 to 30 carbons, R′ is selectedfrom the group consisting of hydrogen, an alkyl radical of from about 1to 6 carbons, and an alkyl alcohol radical of from about 1 to 6 carbons,and R″ is an alkyl alcohol radical of from about 1 to 6 carbons, whereinsaid ester and said molecule are present in said process additive in aratio of said ester to said amide of from about 0:1 to 10:1.
 13. Theprocess additive of claim 12 wherein said molecule is stearamidemonoethanolamine.